docs: def partsphere(self, x):
          """Sphere (squared norm) test objective function"""
          self.counter += 1
          # return np.random.rand(1)[0]**0 * sum(x**2) + 1 * np.random.rand(1)[0]
          dim = len(x)
          x = array([x[i % dim] for i in xrange(2 * dim)])
          N = 8
          i = self.counter % dim
          # f = sum(x[i:i + N]**2)
          f = sum(x[np.random.randint(dim, size=N)]**2)
          return f